/* 层级大小
[z-normal] {
  z-index: 1;
}

[z-top] {
  z-index: 1000;
}

[z-popper] {
  z-index: 2000;
}
-------------------------- */
@each $style in (normal $index-normal, top $index-top, popper $index-popper) {
  [z-#{nth($style, 1)}] {
    z-index: #{nth($style, 2)};
  }
}